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A novel blue-emitting phosphor, Na0.34Ca0.66Al1.66Si2.34O8:Eu2+ (NCASO:Eu2+), was prepared by a wet chemical synthesis method based on the hydrolysis of tetraorthosiliate (TEOS) and confirmed the formation of NCASO:Eu2+ from Rietveld analysis. Photoluminescence (PL) results showed that the phosphor can be efficiently excited by UV light from 250 to 420 nm, and emitted bright broad blue emission, which has maximum intensity at around 445 nm. Under 365 nm excitation, the PL emission intensity area of optimized NCASO:Eu2+ was found to be 99.72% of that of a commercial BaMgAl10O17:Eu2+ (BAM:Eu2+) phosphor. Moreover, the optical absorbance, internal quantum efficiency, and external quantum efficiency of NCASO:Eu2+ were calculated to be 112%, 94%, and 105% of that of the commercial BAM:Eu2+ phosphor, respectively. The WLEDs were fabricated using the blue NCASO:Eu2+ phosphor, a green-emitting β–SiAlON:Eu2+, and a red-emitting CaAlSiN3:Eu2+ phosphors with a near-UV chip. The WLED device exhibited an excellent color–rendering index Ra of 94 at a correlated color temperature of 5956 K with CIE coordinates of x = 0.323, y = 0.335. These results suggest that NCASO:Eu2+ is a promising blue-emitting phosphor for UV LED applications.